Barrier layers are used in electronic devices such as semiconducting devices, printed circuit boards, IC substrates and the like to separate layers of different composition and thereby prevent undesired diffusion between such layers of different composition.
Typical barrier layer materials are binary nickel alloys such as Ni—P alloys which are usually deposited by electroless plating onto a first layer of a first composition followed by deposition of a second layer of a second composition onto the barrier layer.
Another application of barrier layer materials in electronic devices is as a cap layer which is e.g. deposited onto copper to prevent corrosion of copper.
Ternary and quaternary cobalt alloys became of interest as barrier layers or cap layers because of a better barrier functionality compared to binary nickel alloys. Said cobalt alloys are also deposited by electroless plating.
An aqueous, alkaline plating bath for deposition of ternary and quaternary cobalt alloys comprising polyphosphoric acid or salts thereof as a grain refiner is disclosed in U.S. Pat. No. 7,410,899 B2.
An electroless plating bath for deposition of cobalt-based alloys useful as cap layers is disclosed in WO 2007/075063 A1. The plating bath compositions disclosed therein comprise a phosphorous precursor selected from phosphates and hydrogen phosphates, and dimethylamine borane or borohydride as reducing agent. Stabilising agents employed are one or more of imidazole, thiazole, triazole, disulfide and their derivatives.
A plating solution for electroless deposition of cobalt comprising a combination of mercury ions as a primary stabilizing agent and an acetylenic compound such as propargyl alcohol as a secondary stabilizing agent is disclosed in U.S. Pat. No. 3,717,482. The metallic deposit obtained from such a plating bath composition contains mercury.
The patent document U.S. Pat. No. 3,790,392 discloses plating bath compositions comprising formaldehyde as the reducing agent and a propargyl-type additive for electroless deposition of copper metal.
Plating bath compositions comprising formaldehyde as the reducing agent and a polyether adduct of an alkine alcohol and an alkylene oxide for electroless deposition of copper metal are disclosed in U.S. Pat. No. 3,661,597.
The patent document U.S. Pat. No. 4,036,709 discloses acidic plating bath compositions comprising a reaction product of epoxides with alpha-hydroxy acetylenic alcohols for deposition of cobalt alloys by electroplating.
Acidic plating bath compositions comprising diethylaminopropyne sulfate for electroplating of cobalt or nickel-cobalt alloys are disclosed in U.S. Pat. No. 4,016,051.
The patent document U.S. Pat. No. 4,104,137 discloses acidic plating solutions comprising acetylenically unsaturated sulfonates for electroplating of iron-cobalt alloys. Co—W—P alloy barrier layers having a tungsten content in the range of 0.06 to 0.2 wt. —% are disclosed in U.S. Pat. No. 5,695,810. The plating bath disclosed further comprises 50 mg/l polyethoxynonylphenyl-ether-phosphate.